With increasing development of science and technology, electronic devices become more and more popular to users. The widely-used electronic devices include for example desktop computers, notebook computers, smart phones, tablet computers, or the like. Each of these electronic devices has a display screen for displaying an image of the electronic device. Consequently, the electronic device can be operated by the user through the display screen.
For example, the portable electronic device (e.g. the notebook computer, the smart phone and the tablet computer) is a small size and easily carried. Consequently, before the user sleeps, the user usually lies in bed and operates the portable electronic device. Generally, the brightness value of the light source near the bed is very low. Otherwise, the portable electronic device is used in a dark environment without turning on the light source because the display screen of the electronic device can emit light beams.
The display screen of the electronic device is illuminated by the light beams that are emitted from an illumination module within the electronic device. Consequently, the image is displayed on the display screen and the light beams are outputted from the display screen. In case that the ambient light source is dim or the environment is dark, the light beams outputted from the display screen are detrimental to user's eyes and thus the user is readily suffered from vision impairment. Moreover, the long-term injury of the user's eyes may easily lead to macular degeneration of the user's eyes. Consequently, when the electronic device is operated in the dim or dark environment, the user only has to reduce the brightness value of the display screen of the electronic device or turn off the light source in order to reduce the injury of the user's eyes by the light beams of the display screen.
However, the user is only able to roughly reduce the brightness value of the display screen. When the day dawns or the ambient light source is sufficient, the user has to increase the brightness value of the display screen again. Since the processes of repeatedly reducing and increasing the brightness value of the display screen are inconvenient, the user is usually unwilling to reduce the brightness value of the display screen in the dim or dark environment because of laziness. Moreover, before the brightness value of the display screen is reduced, the user has to memorize the current brightness value of the display screen. Consequently, if necessary, the brightness value of the display screen can be restored to the original brightness value. Since the way of memorizing the current brightness value of the display screen is troublesome, the user is usually unwilling to memorize the current brightness value of the display screen.
Therefore, there is a need of providing an easy-to-use luminance adjusting method for a display screen of an electronic device in order to overcome the above drawbacks.